Hundreds of survivors of the world's worst industrial disaster burned effigies of two Olympic officials on Friday to protest against Dow Chemical's sponsorship of the London Games.

The protests were on the eve of the 27th anniversary of the disaster in Bhopal, India, where a Union Carbide pesticide plant leaked lethal gas that killed an estimated 15,000 people and maimed tens of thousands more.

Nearly 200 people, some carrying banners that said "Down with London Olympics" and "We want justice", marched to the now-abandoned plant. They burned effigies of Sebastian Coe, the chairman of the London organising committee, and Vijay Kumar Malhotra, the head of India's Olympic organising committee.

Dow bought Union Carbide in 2001 and has always maintained that legal claims regarding the gas leak were resolved when Union Carbide paid $470m as compensation for those killed or injured. The Indian government is seeking an additional $1.7bn (£1.1bn) for the victims from Union Carbide, and activists accuse Dow of not cleaning up contamination in Bhopal.

Shivraj Singh Chauhan, the chief minister of Madhya Pradesh state where Bhopal is located, last month wrote a letter to India's sports minister, Ajay Maken, asking that the country boycott the London Olympics. More than 20 Indian Olympic athletes have also urged the organisers to end Dow's sponsorship of the Games, which includes a curtain-style wrap around the Olympic Stadium.

This week Malhotra said India had no intention of keeping its athletes away from the games. London Olympic organisers have said they will not change their position on Dow's sponsorship.

Five Bhopal victims' rights groups have said they will stop all trains that pass through Bhopal on Saturday to draw attention to their demands. They say the Olympic sponsorship deal gave undue publicity to a company that was refusing to clean up the toxic contamination of soil and groundwater in Bhopal.